Electric incandescent lamp

ABSTRACT

A regenerative cycle electric incandescent lamp which contains tribromosilane and an inert gas as a transport gas. The lamp, which has a lifetime up to 250 hours with an efficiency of 20 lumens per watt, remains bright until the end of its life.

United States Patent [72] Inventor Germain Relni T'Jampens Eindhoven, Netherlands [21 Appl. No. 834,099

[22] Filed June 17, 1969 [45] Patented June 15, 1971 [73] Assignee U.S. Philips Corporation New York, N.Y.

'[ 32] Priority June 22, 1968 [33] Netherlands [54] ELECTRIC INCANDESCENT LAMP 2 Claims, 2 Drawing Figs.

[52] U.S.Cl 313/174,

[51] lnt.Cl. H0lk 1/50 [50] Field of Search..... 313/174, 176,179,185, 222, 223

[56] References Cited UNITED STATES PATENTS 3,418,512 12/1968 TJampens et a1 313/222 X Primary Examiner-Raymond F. l-lossfeld Attomey-Frank R. Trifari ABSTRACT: A regenerative cycle electric incandescent lamp which contains tribromosilane and an inert gas as a transport gas. The lamp, which has a lifetime up to 250 hours with an efficiency of 20 lumens per watt, remains bright until the end of its life.

INVENTOR.

GERMAIN R. T'JAMPENS ACF/V The invention relates to an incandescent lamp including a tungsten filament body which contains a volatile compound as a reactive transport gas containing bromine and hydrogen and in which the distance from the filament body to the wall of the envelope is so proportioned that the temperature of the wall of the envelope throughout the surface is at least 300 C. during operation of the lamp.

In an incandescent lamp containing bromine and hydrogen in the correct ratio and quantity the wall of the envelope remains bright until the end of the life of the lamp which is determined by the life time of the filament body. This is a result of a cyclic chemical process in the lamp during operation, in which tungsten which evaporates from the filament body is converted by a reaction with bromine into a compound which is still volatile at the lowest temperature occurring in the lamp during operation. The volatile tungsten bromine compound decomposes in the vicinity of the filament body. A cycle is obtained in this manner. If there is sufficient hydrogen in thelamp, tungsten or molybdenum parts (current supply wires, supports) are not attacked or only slowly attacked by bromine at comparatively low temperatures. The gas mixture in the lamp must be free or substantially free from oxygen. In fact, if there is oxygen in the lamp, the so-called water cycle occurs which causes an increased transport of tungsten to the wall of the envelope in the form of a volatile tungsten oxide. A double conversion may take place at the wall while forming a volatile tungsten bromide and water. The transport of tungsten oxide to the wall of the envelope may, however, become so great under unfavorable circumstances that the quantity ofhydrobromic acid available at the wall is insufficient to completely convert the tungsten oxide.

The presence of oxygen can be neutralized at least at the beginning of the lifetime of the lamp by dosing bromine and hydrogen in the lamp fully or partly in the form of a alkylbromide. When switching on the lamp the compound decomposes into carbon and hydrobromic acid which, in turn decomposes into bromine and hydrogen in the vicinity of the filament. The deposited carbon reacts with the tungsten filament while forming tungsten carbide and with oxygen while forming an oxide of carbon. Yet, a water cycle appears to occur after some time in such a lamp.

It was found that for these lamps of this kind having a lifetime of the filament body of up to 250 hours and an efficiency of 25 lumen per watt or more it is advantageous if the reactive transport gas consists of tribromosilane (SiHBr When using this reactive transport gas, neither deposits of silicon arise on the wall nor a detrimental influence on the filament spiral by the formation of silicides is found.

The invention is based on the recognition of the fact that tetrabromosilane (SiBn) is formed during the decomposition of bromosilanes containing hydrogen. Only when using tribromosilane it appears that upon the decomposition there is enough hydrogen and bromine available to maintain a cycle.

The SiBr is volatile in the lamp and may function as a getter for oxygen and water vapor which are detrimental for the cycle; upon reaction with SiBr,, bromine or hydrobromic acid is formed.

Depositions of SiO, are not available.

SiHBr is preferably used in such a quantity that the partial pressure thereof lies between L5 and 6 torr.

Under these circumstances a longer lifetime of the lamp is found to be possible. This must probably be ascribed to the presence of SiBn. An equivalent compound: CBr, is not formed during operation in a lamp containing CH,Br,.

The invention will further be described with reference to a few examples and two embodiments of lamps having a comparatively short lifetime, thus in which a great brightness and luminous flux are important matters. In such lamps the physical lifetime of the filament body, which is a function of the temperature and the mggration caused thereby of tungsten along the filament body mm the hottest areas to colder areas on the filament body, and the chemical lifetime of current supply wires and supports, which is dependent on the attack by bromine, are proportioned in such a manner that the lifetime of the lamp is equal to the lifetime of the filament body. This may be achieved by a correct choice of the geometry of the said metal parts.

FIG. 1 is a cross-sectional view of a photolamp.

FIG. 2 is a cross-sectional view of a projection lamp.

EXAMPLE I The photolamp of FIG. 1 consists of an envelope 1 of quartz containing a tungsten spiral 2 as a filament body; supports are indicated by the reference numeral 3 and consist of a fiat wire spiral. When loading with 225 volts, the power output was l,000 watt, the luminous flux was 32,000 lumen and the efficiency was 32 lumen per watt, the color temperature was 3,400 K.

The lifetime was at least 15 hours in case of a gas filling up to a pressure of 700 torr from a mixture of 8 percent by volume of nitrogen, l 1 percent by volume of CHgBfz.

The lifetime was at least 20 hours in case of a gas filling up to a pressure of 700 torr from a mixture of argon and Sil-lBr (partial pressure 3.4 torr).

EXAMPLE n The projection lamp of FIG. 2 includes a filament spiral 5 of tungsten in an envelope 4 of quartz.

When loading with 24 volts, the power output was watt, the luminous flux was 5,000 lumen and the efficiency was 32 lumen per watt, the color temperature was 3,400 K.

The lifetime was at least 50 hours in case of a gas filling up to a pressure of 2.3 Atm from a mixture of argon and Cl-l,Br, (partial pressure between 10 and 12 torr).

The lifetime was at least l00'hours in case of a filling up to a pressure of 5 Atm with a mixture of argon, nitrogen and SiHBr which contains 4 percent by volume of nitrogen and SiHBr, up to a partial pressure of 5.3 torr.

Lamps according to example II and according to example I remained bright until the end of their life which was invariably reached by the burning through of the filament spiral in one of the hottest areas. Neither the lamps of the type of example I, nor the lamps of the type of example ll showed blackening due to deposition of silicon.

What I claim is:

l. A regenerative cycle electric incandescent lamp comprising an envelope, a tungsten filament body within said envelope, the distance from the filament body to the wall of the envelope being so proportioned that the temperature of the wall of the envelope throughout the surface is at least 300 C. during operation of the lamp, and a mixture of tribromosilane Sil-lBr and an inert gas filling said envelope.

2. An electric incandescent lamp as claimed in claim 1, characterized in that the partial pressure of the tribromosilane lies between 1.5 and 6 torr. 

2. An electric incandescent lamp as claimed in claim 1, characterized in that the partial pressure of the tribromosilane lies between 1.5 and 6 torr. 